1. Field of the Invention
The present invention relates to a base transceiver station for forming radio zones in a mobile communication system and setting channels under the control of a base station control office and to a radio subsystem comprising such a base station control office and base transceiver stations.
The code division multiple access (CDMA) system has a high degree of secrecy and the property of being resistant to the effect of interference and disturbance in the radio transmission paths. Further, CDMA is now also being positively applied to mobile communication systems able to hold speech states while terminal units (mobile station) scattered throughout a radio zone are moving and able to switch (hand off) channels during speech since the technique for realizing control of the transmission power having a high response and precision has recently been established and an effective utilization of radio frequencies has become possible.
2. Description of the Related Art
As will be explained in detail later by using the drawings, in an example of the related art, when there are several radio zones covering a specific point from which a successful call can be made or several base transceiver stations receiving radio waves in parallel from a mobile station at a level enabling demodulation (including reverse spread spectrum processing) and decoding, there is a greater possibility of an increase in the number of frames given overlappingly from the base transceiver stations to the base station control office and also an increase in the traffic transmitted via communication links.
The transmission rate of these communication links, however, must be a rate high enough so that the loss probability of calls which may occur from the mobile stations at the busiest time periods can be suppressed to less than a predetermined upper limit and communication services can be provided at the desired quality of service.
Accordingly, in the related art, there was a high possibility of limitations being applied to the methods of transmission to be adopted to the communication links and the format of the control signals to be transferred in the process of channel setting, and also running costs becoming high.
Further, in the base station control office, the greater the number of frames given overlappedly, the greater the amount of processing required in the processing for receiving these frames and selecting the frame giving the smallest number ST of error symbols.
Accordingly, in consideration with the above problem, an object of the present invention is to provide base transceiver station equipment and a radio subsystem capable of reducing the amount of traffic in a transmission path formed between a base transceiver station and a base station control office without a major change of the structure.
To attain the above object, the present invention provides a base transceiver station provided with: a radio interface means for forming a radio zone, receiving signals transmitted by a mobile station located in that radio zone based on a channel setting procedure or transmitted in a speech state, and measuring the quality of transmission; an identification information acquisition means for acquiring identification information added to these received signals by a mobile station or identification information indicating a timing when those signals were received; a control means for interfacing with the radio interface means and a communication link formed with base station control equipment which takes the lead in the channel setting; and the control means transmits transmission information given as a signal with a measured quality of transmission exceeding a threshold value among signals received by the radio interface means and the identification information obtained by the identification information acquisition means for this signal to the communication link.